Spark Plug Wire (Lead) And Their Resistances.

One of my spark plug wires is damaged: the internal metal connector [that fits over the end of the spark plug] came loose from the rubber boot. I can still mate the boot over the connector, although the connector does not fit as flush as it did before. However, once inserted, the engine does run and very smoothly. There is still enough tension between the broken connector end and the end piece inside the boot to create an electrical connection and to keep the boot attached to the connector even with the engine running. The timing and idle are the same as before the boot and connector separated.

So, I am in the market for a new spark plug wire set. The current set are an aftermarket set for a 4AFE 1.6 L engine. They were made in West Germany, which means they were made quite some time ago; there is no brand marked on the wire or case, only the place of manufacture. Perhaps they are a Bosch? They were installed in 2005 as part of a tune-up. At the time, I did not have the time to do the tune-up myself, so it was done by a local shop. I also wonder if they were defective, as the 4th plug boot has always rested a bit higher than the others, even after replacing the spark plugs.

When I measured the current set, the plug wire leads measured 1 kilo-ohm at plug #1 and progressively under 1 kilo-ohm for the other leads -- which are much less than the 25 kilo-ohm limit given in the shop manual.

1. Does anyone know what are the typical resistances for 4AFE spark plug leads?
2. Is there any correlation between improved sparking and spark plug lead wire resistance; i.e. lower resistance would mean more current enters the plug and the spark would be stronger?
3. Can anyone recommend a good replacement aftermarket plug wires or perhaps I should go with OEM Toyota?

Shop manual applies to the high impedance stock wiring. Aftermarket can be found to range from almost no resistance (solid core) to low resistance thin wire or spiral wire constructions to high resistance carbon cored or resistor wire sets. Most of this resistance built into the wire is for EMI/RFI suppression.

1. Does anyone know what are the typical resistances for 4AFE spark plug leads?
- Depends on the wires that you use to replace the OEM ones - they can vary from almost zero to 10s Kohms.

2. Is there any correlation between improved sparking and spark plug lead wire resistance; i.e. lower resistance would mean more current enters the plug and the spark would be stronger?
- Depends on whom you ask and the application. For modern, computer controlled, fuel injected applications - running a zero resistance, solid core wire is a bad idea. Would work great for an older carburated platform, but would introduce way too much EMI/RFI noise for a newer car. Solid core = basically no noise suppression. Sometimes you get lucky and the solid core works OK, but that is generally in the minority.

As for sparking "power" - given the duration of the pulse and voltage levels - you are shouldn't treat the wire as a regular conductor. A multimeter that reports a resistance of 1000 ohms for one wire and 10,000 ohms with another - to the ignition system - they might look identical. At this higher potential energy and extremely short time scales - you're basically looking at a high frequency system - so you need to consider reactance and inductance of the circuit. Things like dielectric properties of the cable, conductor diameter, shielding, etc. - all start to play into this.

3. Can anyone recommend a good replacement aftermarket plug wires or perhaps I should go with OEM Toyota?
- Can't beat OEM for reliability and fitment. But that doesn't mean aftermarket is all crap. Just stay away from wires that tout some gimmick - built in capacitors, spiral conductors, magnetic wires, multiple cores, etc. Some like Magnecor, Accel, Crane, Electromotive, Jacobs, Mallory, MSD are all legit manufacturers - but can also cost way more than OEM. House brands at most retail automotive retailers are OK, but quality can be suspect from box to box. I'd actually bring the multimeter with you and buzz out each cable before you leave the store. More times than not - you'll find sets that are significantly different from batch to batch.